Problems caused by home plugs would be reflected in DSL error counters and probably dips in SNRM or, if extreme, in DSL connection drops.
In my experience a blip in a throughput graph is not necessarily indicative of a problem, providing that overall throughput remains adequate.
Blips may of course imply errors and retransmissions but they can also be caused by normal flow control procedures applied by the protocols, or if some other activity is competing with the file download for network bandwidth, or if some other activity is competing for disk or CPU access within the destination PC. If you’re using WiFi for the test then that’s another thing that might cause throughput blips.
Remember too that, depending on sampling rate, the graph may make the blips look worse than they are. Streaming services usually employ buffering that will survive blips, as long as they are short.
I’m not defending home plugs, they have a terrible reputation and I’m sure it’s justified. But in your case, if eliminating the home plugs is a big upheaval then I’m not yet convinced that doing so would eliminate these blips.
You did say earlier that you were getting disconnections every day or so. Is it worth expanding on that, as it might be more indicative of a DSL problem?